linux-toradex.git/kernel/signal.c, branch v3.0.16

ptrace: don't clear GROUP_STOP_SIGMASK on double-stop

2011-11-11T17:36:23+00:00

[This does not correspond to any specific patch in the upstream tree as it was
fixed accidentally by rewriting the code in the 3.1 release]

https://bugzilla.redhat.com/show_bug.cgi?id=740121

1. Luke Macken triggered WARN_ON(!(group_stop & GROUP_STOP_SIGMASK))
   in do_signal_stop().

   This is because do_signal_stop() clears GROUP_STOP_SIGMASK part
   unconditionally but doesn't update it if task_is_stopped().

2. Looking at this problem I noticed that WARN_ON_ONCE(!ptrace) is
   not right, a stopped-but-resumed tracee can clone the untraced
   thread in the SIGNAL_STOP_STOPPED group, the new thread can start
   another group-stop.

   Remove this warning, we need more fixes to make it true.

Reported-by: Luke Macken 
Signed-off-by: Oleg Nesterov 
Signed-off-by: Greg Kroah-Hartman

signal: align __lock_task_sighand() irq disabling and RCU

2011-07-20T18:04:54+00:00

The __lock_task_sighand() function calls rcu_read_lock() with interrupts
and preemption enabled, but later calls rcu_read_unlock() with interrupts
disabled.  It is therefore possible that this RCU read-side critical
section will be preempted and later RCU priority boosted, which means that
rcu_read_unlock() will call rt_mutex_unlock() in order to deboost itself, but
with interrupts disabled. This results in lockdep splats, so this commit
nests the RCU read-side critical section within the interrupt-disabled
region of code.  This prevents the RCU read-side critical section from
being preempted, and thus prevents the attempt to deboost with interrupts
disabled.

It is quite possible that a better long-term fix is to make rt_mutex_unlock()
disable irqs when acquiring the rt_mutex structure's ->wait_lock.

Signed-off-by: Paul E. McKenney 
Signed-off-by: Paul E. McKenney

signal.c: fix kernel-doc notation

2011-06-15T02:12:17+00:00

Fix kernel-doc warnings in signal.c:

  Warning(kernel/signal.c:2374): No description found for parameter 'nset'
  Warning(kernel/signal.c:2374): Excess function parameter 'set' description in 'sys_rt_sigprocmask'

Signed-off-by: Randy Dunlap 
Signed-off-by: Linus Torvalds

signal: sys_pause() should check signal_pending()

2011-05-25T17:22:27+00:00

ERESTART* is always wrong without TIF_SIGPENDING. Teach sys_pause()
to handle the spurious wakeup correctly.

Signed-off-by: Oleg Nesterov

Merge branch 'ptrace' of git://git.kernel.org/pub/scm/linux/kernel/git/oleg/misc

2011-05-20T20:33:21+00:00

* 'ptrace' of git://git.kernel.org/pub/scm/linux/kernel/git/oleg/misc: (41 commits)
  signal: trivial, fix the "timespec declared inside parameter list" warning
  job control: reorganize wait_task_stopped()
  ptrace: fix signal->wait_chldexit usage in task_clear_group_stop_trapping()
  signal: sys_sigprocmask() needs retarget_shared_pending()
  signal: cleanup sys_sigprocmask()
  signal: rename signandsets() to sigandnsets()
  signal: do_sigtimedwait() needs retarget_shared_pending()
  signal: introduce do_sigtimedwait() to factor out compat/native code
  signal: sys_rt_sigtimedwait: simplify the timeout logic
  signal: cleanup sys_rt_sigprocmask()
  x86: signal: sys_rt_sigreturn() should use set_current_blocked()
  x86: signal: handle_signal() should use set_current_blocked()
  signal: sigprocmask() should do retarget_shared_pending()
  signal: sigprocmask: narrow the scope of ->siglock
  signal: retarget_shared_pending: optimize while_each_thread() loop
  signal: retarget_shared_pending: consider shared/unblocked signals only
  signal: introduce retarget_shared_pending()
  ptrace: ptrace_check_attach() should not do s/STOPPED/TRACED/
  signal: Turn SIGNAL_STOP_DEQUEUED into GROUP_STOP_DEQUEUED
  signal: do_signal_stop: Remove the unneeded task_clear_group_stop_pending()
  ...

ptrace: fix signal->wait_chldexit usage in task_clear_group_stop_trapping()

2011-05-09T12:19:54+00:00

GROUP_STOP_TRAPPING waiting mechanism piggybacks on
signal->wait_chldexit which is primarily used to implement waiting for
wait(2) and friends.  When do_wait() waits on signal->wait_chldexit,
it uses a custom wake up callback, child_wait_callback(), which
expects the child task which is waking up the parent to be passed in
as @key to filter out spurious wakeups.

task_clear_group_stop_trapping() used __wake_up_sync() which uses NULL
@key causing the following oops if the parent was doing do_wait().

  BUG: unable to handle kernel NULL pointer dereference at 00000000000002d8
  IP: [] child_wait_callback+0x29/0x80
  PGD 1d899067 PUD 1e418067 PMD 0
  Oops: 0000 [#1] PREEMPT SMP
  last sysfs file: /sys/devices/pci0000:00/0000:00:03.0/local_cpus
  CPU 2
  Modules linked in:

  Pid: 4498, comm: test-continued Not tainted 2.6.39-rc6-work+ #32 Bochs Bochs
  RIP: 0010:[]  [] child_wait_callback+0x29/0x80
  RSP: 0000:ffff88001b889bf8  EFLAGS: 00010046
  RAX: 0000000000000000 RBX: ffff88001fab3af8 RCX: 0000000000000000
  RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffff88001d91df20
  RBP: ffff88001b889c08 R08: 0000000000000000 R09: 0000000000000000
  R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
  R13: ffff88001fb70550 R14: 0000000000000000 R15: 0000000000000001
  FS:  00007f26ccae4700(0000) GS:ffff88001fd00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
  CR2: 00000000000002d8 CR3: 000000001b8ac000 CR4: 00000000000006e0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
  Process test-continued (pid: 4498, threadinfo ffff88001b888000, task ffff88001fb88000)
  Stack:
   ffff88001b889c18 ffff88001fb70538 ffff88001b889c58 ffffffff810312f9
   0000000000000001 0000000200000001 ffff88001b889c58 ffff88001fb70518
   0000000000000002 0000000000000082 0000000000000001 0000000000000000
  Call Trace:
   [] __wake_up_common+0x59/0x90
   [] __wake_up_sync_key+0x53/0x80
   [] __wake_up_sync+0x10/0x20
   [] task_clear_jobctl_trapping+0x44/0x50
   [] ptrace_stop+0x7c/0x290
   [] do_signal_stop+0x28a/0x2d0
   [] get_signal_to_deliver+0x14f/0x5a0
   [] do_signal+0x75/0x7b0
   [] do_notify_resume+0x5d/0x70
   [] retint_signal+0x46/0x8c
  Code: 00 00 55 48 89 e5 53 48 83 ec 08 0f 1f 44 00 00 8b 47 d8 83 f8 03 74 3a 85 c0 49 89 c8 75 23 89 c0 48 8b 5f e0 4c 8d 0c 40 31 c0 <4b> 39 9c c8 d8 02 00 00 74 1d 48 83 c4 08 5b c9 c3 66 0f 1f 44

Fix it by using __wake_up_sync_key() and passing in the child as @key.

I still think it's a mistake to piggyback on wait_chldexit for this.
Given the relative low frequency of ptrace use, we would be much
better off leaving already complex wait_chldexit alone and using bit
waitqueue.

Signed-off-by: Tejun Heo 
Reviewed-by: Oleg Nesterov

signal: sys_sigprocmask() needs retarget_shared_pending()

2011-05-09T11:48:56+00:00

sys_sigprocmask() changes current->blocked by hand. Convert this code
to use set_current_blocked().

Signed-off-by: Oleg Nesterov

signal: cleanup sys_sigprocmask()

2011-04-28T11:01:40+00:00

Cleanup. Remove the unneeded goto's, we can simply read blocked.sig[0]
unconditionally and then copy-to-user it if oset != NULL.

Signed-off-by: Oleg Nesterov 
Acked-by: Tejun Heo 
Reviewed-by: Matt Fleming

signal: rename signandsets() to sigandnsets()

2011-04-28T11:01:39+00:00

As Tejun and Linus pointed out, "nand" is the wrong name for "x & ~y",
it should be "andn". Rename signandsets() as suggested.

Suggested-by: Tejun Heo 
Signed-off-by: Oleg Nesterov 
Acked-by: Tejun Heo

signal: do_sigtimedwait() needs retarget_shared_pending()

2011-04-28T11:01:39+00:00

do_sigtimedwait() changes current->blocked and thus it needs
set_current_blocked()->retarget_shared_pending().

We could use set_current_blocked() directly. It is fine to change
->real_blocked from all-zeroes to ->blocked and vice versa lockless,
but this is not immediately clear, looks racy, and needs a huge
comment to explain why this is correct.

To keep the things simple this patch adds the new static helper,
__set_task_blocked() which should be called with ->siglock held. This
way we can change both ->real_blocked and ->blocked atomically under
->siglock as the current code does. This is more understandable.

Signed-off-by: Oleg Nesterov 
Acked-by: Tejun Heo 
Reviewed-by: Matt Fleming